so adding the correction is acceptable. At 2334Z, weread the left side of the solid band at 33°. Adding theequipment correction of 2° would result in only a 35°corrected angle. Since the correction is less than 45°,the correction is not added, and the 33° elevation angleshould be used.CONVERTING ELEVATION ANGLE TOCLOUD HEIGHT.The operators manual for theGIFFT recorder contains a table for convertingelevation angle to cloud height for units using thestandard 400-foot baseline. A table may be constructedfor your units baseline, if different from the standard,by multiplying the tangent of the elevation anglesfrom 1° through 89° by the length of your baseline, infeet.MaintenanceMaintenance requirements for the RO-546 recorderare described in the operators manual. All calibrationsand electrical checks are performed by base groundelectronics personnel.Aerographers Mates areresponsible for changing the recorder chart paper andreplacing the chart-marking stylus when the old stylusbecomes worn, broken, or bent. Pilot-reported cloudheights that are consistently different from RO-546indicated heights, or other indications of malfunction,should be reported to ground electronics. Backupequipment, such as the ML-121 ceiling light projectorand the ML-l19 clinometer, should be used when theAN/GMQ-13 is out of service.ML-121 CEILING LIGHTPROJECTORThe standard light projector used by the Navy andMarine Corps is the ML-121 ceiling light projector,shown in figure 2-43.This equipment projects anarrow, concentrated beam of light vertically ontocloud bases up to 10,000 feet. An observer, sighting atthe illuminated spot on a cloud base, uses clinometerelevation angle and baseline distance to find cloudheight. The light projector is effective only at night.OperationThe ceiling light projector is activated by a switchlocated in the weather office or outside near theobservation point. The projector must be activated onlywhen conducting a measurement. The high-intensitylight may confuse pilots, both ashore and aboard ship;therefore, you must request permission from yoursupervisor to activate the projector.Figure 2-43.ML-121 ceiling light projector.MaintenanceGround electronics personnel should providemaintenance support for the projector. Maintenanceprocedures are described in NA 50-30FR-521,Handbook, Operation and Maintenance Instructions,Ceiling Light Projector ML-121 and Clinometer ML-119. Recommended operator maintenance includes thefollowing:Weekly cleaning of glass cover plate andinspection and cleaning of drainage/ventilation holes inthe projector housingReplacing lamps that are burned out or haveblackened or sagging filamentsQuarterly checking of lamp alignment and focus,and inspecting the projector to make sure it is levelCLINOMETERClinometers are used to measure the elevation angleof the projected light spot on a cloud base. Two differenttypes of clinometers are used: the ML-119 clinometer,found only at shore stations, and the ML-591/U2-33